The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Internal combustion engines combust an air and fuel mixture within cylinders to drive pistons, which produces drive torque. Air flow into gasoline engines is regulated via a throttle. More specifically, the throttle adjusts throttle area, which increases or decreases air flow into the engine. As the throttle area increases, the air flow into the engine increases. A fuel control system adjusts the rate that fuel is injected to provide a desired air/fuel mixture to the cylinders. Increasing the amount of air and fuel provided to the cylinders increases the torque output of the engine. Typically heated catalysts are used within the exhaust system to reduce certain components of the exhaust gases. Typically the heating comes from burning fuel in the engine. Electrically heated catalysts may also be used. The catalyst operates more efficiently above a certain temperature.
Hybrid vehicles generally have two power sources. The internal combustion engine is a first power source and an electric motor is a second power source. The electric motor is used more often as a power source in city driving where vehicle kinetic energy can be recovered by regenerative braking, converted to electric and chemical form, and stored in a battery, from which the motor is driven. The internal combustion engine is more suitable during highway driving, during which wheel braking and opportunities for energy recovery are infrequent, and the engine operates at its greatest efficiency.
In mixed driving conditions, the electric motor and combustion engine may be used together to transmit power to a transmission input shaft, depending on driving conditions and the magnitude of the battery capacity.
Hybrids experience long periods of engine off-time during idle and driving scenarios. During the period of engine off-time, the catalyst temperature may fall which may require additional heating to obtain the peak efficiency of the converter. Maintaining the catalyst temperature reduces the amount of emissions for a cold start event.